This invention relates to a document shredder for waste materials, and more particularly to a shredder mechanism for shredding intelligence data such as all types of waste documents, drawings and microfilm, waste matter such as newspapers, magazines, books, bankbooks, plastics, rubber and leather, and other kinds of unnecessary material in sheet-like form such as asphalt or the like.
In governmental, banking and industrial circles the destruction and disposal of important confidential documents and other unnecessary papers has been accomplished by finely cutting the waste documents into strips by means of a document shredder in order to preclude the danger of intelligence leaks. However, there is the possibility that the content of the waste documents can be reconstructed since characters and lines remain on these strips. In an effort to overcome this shortcoming, U.S. Pat. Nos. 3,396,914 and 3,529,782 disclose a shredder comprising a feed drum composed of a plurality of disks each having teeth about the periphery thereof, and a shredding drum consisting of a disk having choppers about the periphery thereof, the shredder thus being adapted to shred unnecessary documents into small chip-like fragments. The shredding drum rotates at an extremely high speed with respect to the feed drum and therefore develops a small torque when rotating. Accordingly, the number of sheets of unnecessary documents which can be processed at one time is limited, a disadvantage in that the efficiency of operation is unsatisfactory. The shredder is also noisy since the shredding drum choppers strike the documents at high speed.
U.S. Pat. No. 3,860,180 offers a solution to these problems through the disclosure of a shredder that employs a pair of shredding members each comprising a rotary blade having notches spirally formed on the outer periphery thereof. According to this system, unnecessary documents are finely cut into chip-like fragments by bringing a nose adjacent to a notch of one rotary blade into engagement with the outer periphery of the other rotary blade. Since the documents in this shredder are torn transversely by the nose edge, the documents can not be reliably torn into chip-like fragments but will instead tend to be cut into elongated strips whenever a large number of sheets are introduced or whenever they possess a large tensile strength. There is thus the strong possibility of intelligence leaks since characters or entire sentences remain on these long strips as mentioned above. To improve upon this defect it has been proposed that a groove be provided ahead of the rotary blade notch and that the strips be made to engage with the groove to thus be pulled and torn into pieces. Nevertheless, this expedient has not proved effective. In addition, for the reasons stated above, a shredder of this type does not possess the capability of shredding into the form of chips materials which exhibit a high tensile strength, such as microfilm, plastics, rubber and leather.